Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$100.73	10.299%	$111.1042	$111.10	$111.10	$111.10
Purchase #2	$121.87	12.838%	$137.5157	$137.52	$137.50	$137.50
Purchase #3	$29.94	7.496%	$32.1843	$32.18	$32.20	$32.20
Purchase #4	$137.68	11.588%	$153.6344	$153.63	$153.65	$153.60
Purchase #5	$59.99	10.732%	$66.4281	$66.43	$66.45	$66.40
Purchase #6	$132.94	13.290%	$150.6077	$150.61	$150.60	$150.60
Purchase #7	$105.88	7.442%	$113.7596	$113.76	$113.75	$113.80
7 purchase totals =	$689.03		$765.2340	$765.23	$765.25	$765.20